In networks such as 3GPP LTE and/or universal mobile telecommunications system (UMTS) networks, mobile or wireless user equipment (UE:s) in a cell generally interfere with UE:s in other cells, especially when the same set of radio resources are used in the different cells across the network. This is known as inter-cell interference. Inter-Cell Interference Coordination (ICIC) is a method used to reduce the effect of inter-cell interference. The basic idea of ICIC is to prevent neighbouring UE:s, i.e. UE:s that are in different cells but are close to the particular base station, from using the same radio resources. ICIC can be seen as a scheduling approach, taking into consideration the situation in neighbouring cells. In order to support efficient ICIC, UE measurement and reporting scheme is needed since the radio positions of the UE:s have a significant impact on how much interference is contributed with to the neighbouring cells in the uplink. In addition, inter-cell interference is also increased when a UE is near the cell boarder, i.e. far from it serving base station (also known as NodeB or evolved NodeB (eNB)) but close to the neighbouring cell. This is because such a UE is power controlled, meaning that it will need to transmit with higher power than a UE close to the serving eNB. Suitable UE measurements that can be used for ICIC are handover path loss measurements as these are widely accepted to be useful for a variety of ICIC schemes. An example of such ICIC scheme in LTE for uplink is known as the overload indicator (OI). A working assumption for uplink inter-cell power control is that neighbouring eNBs can control individual UE:s served by that eNB through its scheduler based on the OI and available knowledge, e.g. path loss measurements obtained from ordinary/normal handover measurements and reporting. Thus, path loss measurements used for handover can be used for ICIC when scheduling resources for a UE.
Handover reporting, however, has different objectives so that additional reporting criteria for the ICIC are needed. The handover reports are expected to be threshold triggered. This thresholds will not be the same as for ICIC. As an example, handover typically has a threshold at e.g. 1-3 dB stronger neighbour, whereas for ICIC, a threshold of e.g. 6-20 dB weaker neighbour cell than the connected cell can be used. Furthermore, handover reporting can be triggered at one defined threshold, but for ICIC a more continuous measure covering a range of path losses and path loss differences is usually needed.
In e.g. the technical specification issued by 3GPP denoted TS 25.321 v.7.4.0 and entitled: “Medium Access Control (MAC) protocol specification (Release 7)”, it is stated that the serving and neighbour cell path loss (SNPL) may be used by the NodeB of the serving cell to assist with its estimation of the degree of inter-cell interference each UE will generate and hence the absolute grant power and physical resources to assign/schedule.
A drawback with the solution described above is that the SNPL is always sent together with buffer status. The amount of resources to assign depends on the service and user interaction whereas the SNPL measurements change based on mobility of the UE. This can result in frequently SNPL reporting and a large overhead. It can also result in missing SNPL information due to that header reporting is configured to be sparse.
In U.S. patent application No. 60/895,580 it is described a solution on how to reduce interference in a network. In this prior art, the solution is to tie the uplink (UL) scheduling request and handover measurements to each other. Hence, the UE simultaneously as transmitting the UL scheduling request also transmits serving cell and neighbouring cell measurement information. The NodeB serving the UE can then make a decision and order the UE to perform a handover prior to sending data and thereby moving the UE into the new cell (with respect to signal strength) prior to sending the data. The NodeB takes the handover decision before the UE has triggered the handover. This way a faster HO decision is taken thus leading in reduction in the amount of interference the UE generates in the neighbouring cell.
A drawback with this prior art solution is that unnecessary radio interface load is generated in the network because each UE simultaneously needs to transmit and report handover measurements and scheduling requests each time such UE has some data to send. Furthermore the handover triggering and reporting criteria differs from the criteria for ICIC as described above. In addition, the radio environment can change during scheduling grants especially with persistent and semi-persistent scheduling. Persistent scheduling is a scheduling of resource blocks (granted to a UE (or a group of UEs)) that is valid for a relatively long time period ahead, and semi-persistent scheduling is a scheduling of resource blocks (granted to a UE (or a group of UEs) that is valid for as long as more data is sent within a predetermined time period of last sent data and expires if no data is sent within the predetermined time period. Thus in the case of persistent and semi-persistent scheduling, no scheduling request(s) are sent from the UE and hence no handover report.
In the international patent application No. PCT/SE2007/050257 there is disclosed a method in a base station for predicting interference contribution, when scheduling an uplink data transmission from a first UE being connected to the base station. In this scenario, the UE is located in the neighbourhood of a neighbouring cell served by a neighbouring base station. Thus, the UE is close to the cell boarder. The method suggested in this prior art comprises the steps of: obtaining signal strength measurements from the UE (the signal strength measurements are based on a reference signal received by the UE from the neighbouring base station); receiving a resource scheduling request from the UE for the uplink data transmission, scheduling uplink resources for the requested uplink data packet transmission; determining transmission power to be used for the scheduled uplink resources; and estimating an interference prediction contribution based on the determined transmission power and the obtained signal strength. This prior art does however not describe what criteria are used for the reporting.